1. Field of the Invention
The purpose of this invention is to provide 1) impregnated wood materials introducing a fire retardant property to wood products, 2) impregnation of other cellulosic materials, such as paper and cloth, and other organic compounds in such a way as to allow their intended functions while reducing the risk of flammability, 3) impregnated wood materials introducing increased strength to wood products, and 4) impregnated wood materials introducing decreased solubility of the constituents of the final product thereby providing moisture and leachate and weather resistant products.
Alkali metal silicates, applied to various products can be used to impart fire retardant properties, and this fire retardant property can be maintained and enhanced by simultaneous or subsequent treatment to cause the alkali metal silicates to become water insoluble, thus greatly increasing the applicability and utility of products treated with alkali metal silicates, and also providing a product with improved strength and durability.
2. Description of Related Art
I studied fire retardants and found a new approach for creating water insoluble fire retardants by carefully observing and investigating my burn tests!
In my early work I learned that we really live in a tinderbox surrounded by flammable materials. This became most obvious to me when my own house caught fire two years ago. This is what originally got me interested in fire retardants.
Many organic and inorganic substances for fire retardants have been studied (Lyons 1970, Grayson, 1985). For organic fire retardants two of the major approaches are: 1) converting flammable substances such as common solvents into inflammable substances by reacting them with chemicals such as halogens (e.g., bromine), which are then infused into the wood, and 2) using similar approaches to chemically modify the flammable material such as plastic resin and render the material less flammable. Both of these techniques are expensive and produce toxic fumes. There are many inorganic substances studied for fire retardant properties.
For some fire retardant methods good results are reported in literature. A simple trip to the local lumberyard showed however, that there are apparently very few fire retardants for wood in widespread consumer use. All samples I tested that were purchased at random from local lumber yards burned rapidly.
I chose to study the alkali metal silicate, sodium silicate, because it is relatively cheap, it is inherently nonflammable, there is no discoloration displayed by sodium silicate, and I felt that the adhesive properties of sodium silicate would be useful in some way. Using sodium silicate as a fire retardant, which seemed to me an excellent idea, was apparently not shared by others in the field of fire retardants.
Sodium silicate is only of historical interest in the literature and is not studied at present due to the following facts: 1) sodium silicate is highly water soluble and leaches readily, 2) if you apply it to wood, within a few months it will have completely peeled and chipped away, 3) with air exposure it will form a granular powder that is very irritating to the eyes and hands.
The scientific consensus of sodium silicate is best summed up by Lyons (1970):
"The processes . . . (as protective coating or immersion baths) . . . and its results are principally physical, not chemical in nature and thus no detailed chemical discussion is warranted here." PA1 Pressed with a hot metal plate (200.degree. C.) over a thin layer of mica, PA1 Pressing a hot metal plate directly on the surface of the sample, 60 sec PA1 Holding a hot metal plate (200.degree. C.) 1 mm above the surface of the sample, PA1 Baked in an industrial convection oven at 260.degree. C. for five minutes, PA1 Heated for five minutes in a microwave, PA1 Quickly dipped in water (5 sec), then placed in an oven preheated at 260.degree. C. for five minutes. PA1 Heated for five minutes in a microwave, wet sample, no prior air drying PA1 Baked in an industrial convection oven at 260.degree. C., wet sample, no prior air drying PA1 Baked in a standard oven at 150.degree. C. for an 1.5 hours, PA1 Dipped in distilled water for 5 seconds, baked 5 min@260.degree. C. PA1 convection oven@500.degree. F., 6.5 min. PA1 microwave 11 minutes, in 3-4 minute intervals, with 1 minute cooling periods PA1 microwave 11 minutes, in one interval PA1 size 2 cm.sup.3, microwave 5 min PA1 size 1.times.4.times.12 inches, microwave 24 min in 4 min increments PA1 craft sticks, broiled 5 min@260.degree. C., then foam scraped from surface PA1 1.times.4.times.12 inch pine, broiled 5 min@260.degree. C., then foam scraped from surface
This was the extent of the knowledge in the field, research studies in the field turned to other materials and to a few combinations with other substances such as tar.